Periodic reverse current electroplating apparatus



June 26, 1951 G. w. JERNSTEDT 0 9 0 8 5 5 S 2 U T W P P A G .m T A L P mm L E T W C E s R E V E R C I D O I R E P 2 Sheets-Sheet 1 Filed Dec.ll, 1947 INVENTOR George W'Jernsed.

June 26, 1951 G. w. JERNsTDT 2558,090

PERIODIC REVERSE CURRENT ELECTROPLATING APPARATUS Filed Dec. ll, 1947 w2 Sheets-Sheet 2 WITNESSES:

` lNvENToR W i George' W Jernsedf.

Patentted June 26, 1951 UNITED S'TATES PATENT. OFFICE 'I'ERIODIC REVERSEvCURRENT'ELECTRO- PLATIN G APPARATUS George W. Jernstedt, Pittsburgh,Pa., assignor to Westinghousc Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application December 11, 1947, serialNo. 791,027

5 Clams. 1

This invention relates to .anxelectroplating conveyor apparatus, and inparticularto apparatus constructed to function automatically tolelectrodeposit metal on members by applying thereto a periodic reversecurrent.

There is disclosed in my copending patent application SerialNo. 610,107,filed August 10, 1945, now Patent 2,451,341, that metal'may beelectrodeposited with. considerable improvement in quality and speed ofplating by employing a periodically reversed current. While the use ofspecial current reversing mechanisms, such vasv reversing switchesor'specially Wound generators, may be resorted to in order to secure aperiodically reversed current, the initial cost and maintenance areoften high. Furthermore, there are many conventional conveyorizedelectroplating installations that Would require considerable additionalequipment and rebuilding to convert them to periodic reverse currentplating. It is desirable .to employ conventional apparatus as far aspossible in any electroplating apparatus and to convertA it to a reversecurrent plating set up with the minimum of alteration or change. Inparticular, it would be desirable to employ conventional sources ofcontinuous direct current, such, for example, as a direct-currentgenerator or a rectifier, and to make a relatively simple alteration toproduce a reverse current plating installation therefrom.

According to -the present invention, it has been found possible by arelatively simple change in conventional electroplating systemsemploying conveyors to enable them to `electroplate members with aperiodic reverse current and certain exceptional advantages have beenfound to follow.

The object of the present invention is to provde an electroplatingconveyor apparatus for automatically periodically r-eversing the currentapplied to members being plated during the operation thereof.

Another object of the invention is to provide an electroplating conveyorapparatus with an electrical conductor provided With alternate anodicand cathodic current Sections whereby work being plated has appliedthereto periodically reversed current.

Other objects of the invention will in part appear obvious and will inpart appear hereinafter. For a better understanding of the nature andobjects of the invention, reference should be had to the followingdetailed vdescription and drawings, in which:

Figure 1 is a plan view of an electroplating conveyor apparatusconstructed in accordance with the invention;

Fig. 2 is a fragmentary view partlyin section of the conveyor of Fig.1';

- Fig. '3 is a view in perspective, partly insection, showing details;

Fig. 4 is a 'schematic view of'a modified form of the invention;

Fig. 5 is a side elevation, 'partly broken of a modified form ofconveyor apparatus; and

Fig. 6 is a schematic view of another modification of the invention.

As disclosed in my copending Patent 2,451,341, the electroplatingprocess and electrodeposits produced may be greatly improved byapplying'to base members beingelectroplated a periodically reversedcurrent in 'which thebase member is subj'ected to aseries of alternatecathodic and anodic current pulses, each extending over a predeterminedshort' interval of' time. In partie'- ular, the cathodic currentintervalshould be for a time of not over v4b seconds whereby an increment ofmetal is i'deposited on the base member. The 'cathodic current issucceeded by an anodic current which is' of a su'fiicient currentdensity and is applied for a period of time sufiicient to deplateunsound and inferiozmetal from the increment plated duringthel precedingcathodic portion of the cycle. After the 'preceding increment ispreferenti'ally partially deplated, by the anodic current, therebyleaving smooth, sound metal, a second pulse of cathodic current is'applied to deposit more metal and, in turn, is followed by asucceedingvanodic current Vpulse to deplate unsound `and inferior metalfrom this latter increment. This cathodic-anodic current cycle isrepe'ated until the required amount of metal has been'plated. i Inparticular, the anodic portion of the cycle should be at such a currentdensity and for a s'ufficient period of time to apply at least 4% of thecoulombs'applied to the base member during the cathodic or'platingportion of the cycle but not exceeding approximately of the coulombsapplied during the rcathodic portion of the cycle. For plating mostvmetals, the best results are'se'cured from' vthe standpoint of totalmetal plated'and quality of metal plated where the anodic current`portion applies to the base member from '20% to40% of the coulombsapplied during the cathodic portion of the cycle. Usually the currentdensity during the'cathodic and anodic pulse is the" same and the timeintervals lare adjusted' to secure the proper ratio of eoulombs.

The periodic reverse' current cycle hasv given good results whenv'em'ploy'ed for'plating copper, brass, zinc, cadmium, silver, gold,nickel, iron,

cobalt and various alloys of these metals. Electrodeposits are producedwith periodic reverse current that are smoother, brighter and Sounderthan produced by conventional continuous direct current, also the speedof plating can be greatly increased. The cycles which have given goodresults in practice will vary to some extent with the metal being platedand the nature of the electrolyte. Periodic reverse current plating hasbeen found to have the following advantages over con'- tinuousdirect-current plating with regard to the following factors:

1. An increase in the rate of metal deposited per unit time.

2. An increase in the density of electrodeposited metal.

3. Increased surface brightness of the electrodeposit.

4. Plating of metal smoother and sounder than the base member. z

5. Heavier deposits of acceptable quality.

6. A decreased porosity.

7. Better metal distribution over base member.

The periodic reverse current process is fiexible and may be so carriedout by varying the proportion of the anodic and cathodic current cyclesto greatly emphasize one or more of the above '7 features.

More specifically, for plating copper, brass and silver from aqueouscyanide solutions, it has been found that the Optimum results aresecured with a current cycle having a cathodic interval of from 2 to 40seconds, and an anodic interval of from 1/!2 to 10 seconds, wherein theanodic' current applies from 10% to 50% of the coulombs applied duringthe cathodic interval. For plating nickel and cobalt, as disclosed inthe copending application 759,796, filed July 9, 21947, now Patent2,470,775, the cathodic interval should be less than 2 seconds, andpreferably from 1/2 to one hundredth of a second. while the anodicinterval is approximately 1/2 to 1/25 of the cathodic period, thecoulombs during the anodic portion of the cycles varying from 4% to 60%of the coulombs during the cathodic portion.

According to the present invention, conveyorized electroplatingapparatus is so constructed and arranged that it automatically applies aperiodically reverse current to members being plated during theoperation thereof. The conveyorized electroplating apparatus is suppliedwith conventional continuous direct-current from a suitable source, suchas a generator, rectifier, battery or the like.

Referring to Fig. 1 of the drawings, there is illustrated a conveyorizedelectroplating machine which consists of a tank of glass, rubber coveredmetal, Wood or other material unaffected by an electrolyte l2 from whichmetal is to be plated contained therein. Anode conductor bars |4 aredisposed at the outer side walls and at the inner portions of the tankfor Supporting a plurality of anodes Hi of the metal to beelectrodeposited on base members being processed. The number and spacingof the anodes are in accordance with well known practice. The conveyormechanism includes two sprocket Wheels 4 23 may be supplied withinsulating bushings to prevent fiow of current to them or they may beoomposed entirely of a resin laminate which is electricallynon-conductive. The links 24 each carry a movable support 26 from whichthere hangs a work holding rack 28 having a plurality of arms 30 onwhich base members 32 may be hung. A great variety of racks are employedin the industry and the illustration in the drawings is only exemplary.In general, electrical current passes from the Support 26 to the rack28, thence to the arms 30 and thence to the base members 32 which, whenthus electried while in contact .with the electrolyte will be subject toelectrolytic action. A guide and support rail 34 assists the supports 26to carry the load of the electroplated work without irnposing an unduestrain on the p cham 22.

IB and 20 disposed one at each end of the tank The movable supportsoBare disposed to move in slidable contact with'a conductor bar 38. Thebody of the conductor bar 38 carries continuous direct current and ismaintained at a negative or cathodic potential. At spaced intervals theconductor bar 38 is recessed thereby leaving raised Sections 39, andSections or portions 40 electrically insulated by insulation 42 aredisposed in the recesses. The surface of the conductor bar thereforepresents alternate Sections 39 and 40. Both the conductor bar 38 and theSections or portions 40 may be oomposed of copper or other goodconductor material. The Sections 40 are each connected to the positiveterminal of a continuous direct-current source whereby they are keptanodic. Any Supports 26 in contact with the surface of a section 39receive cathodic current and members 32 supported therefrom will havemetal deposited thereon from the electrolyte |2. When a movable support26 comes into slidable engagement with one of the Sections 40, thecurrent in the support becomes anodic and metal plated on the members 32will be deplated until the support 26 moves out of engagement with thesection 40.

The spacing between the supports 28 is so adjusted with relation to thespacing and dimensions of the cathodic Sections 39 and the anodicSections 40 that at any given time over the entire length of theconductor bar 38 a relatively constant number of the supports are incontact With the Sections 40 and the remainder, except for a very smallproportion riding on the insulation 42, are in contact with the cathodicportion 38. This feature can be Secured by spacing the supports 25 by adistance which is not a multiple of the total distance of an anodicsection 40 plus a oathodic section 39. In this manner, there is obtaineda relatively constant anodic and cathodic current fiow withoutsubstantial fiuctuations during the operation of the apparatus. TheSections 40 are of lesser length in the direction of travel ofthemovable supports 26, than the cathodic Sections 39 therebetween, thelengths being proportioned to the desired ratio of cathodic current tothe anodic current in the periodic reverse current cycle. In general,less than half of the supports 23 are in contact with the Sections 40and more than half are in` contact with the Sections 39. Thus it will beapparent that during movement of the conveyor, each support 26 Willbecome alternately energized With cathodic and'anodic current whereby oncontacting section 39, an increment of metal is plated on a base member32 for a period of time depending on the speed of movement of the chain22 and the. length of a Section 39 and then on passing into slidablecontact with a section 40, the support and base member is renderedanodic to deplate a portion of the metal plated thereon during thepreceding cathodic interval. In this manner, the members 32 are platedwith a periodic reverse current with all the advantages ensuingtherefrom as previously set forth.

While supports 26 carry racks, it is feasible to mount a rotatingplating barrel on the support for plating small articles in bulk.

Referring to Fig. 3 of the drawings, there is illustrated in detail amodified form of a conductor bar for supplying reversed current. Themovable support 26 is operated for slidable movement. Paralleling thedirection of such slidable movement is a cathodic conductor bar mountedon an insulating support 102, and having recesses in the upper surfacetherein at spaced intervals with insulating material |06 disposed in therecesses fiush With the upper surface' The conductor bar li thereforehas a series of exposed conducting sections 504. The insulating material106 may be a resinous material, such as phenol formaldehyde resinlaminate or other suitable substance. Also mounted on the insulatingsupport 02 and paralleling the bar |00 is an anodic conductor bar |l0also having recesses therein but at staggered alternating intervals withrespect to the recess in the bar 100, the recesses being filled with aninsulating material I 08. The conductor bar presents a series of exposedconducting Sections I i I. The upper surfaces of the bars il and U0therefore, present a series of alternating conducting Sections 101i andHI in the lengthwise direction. The support 26 is provided with a box VI|2 having two brushes lli and HB, which may be carbon brushes. Springs116 and l20 urge the brushes IM and M8 into engagement with the'conductor bars i IB and E00, respectively. A source of direct current522 is suitably connected to the two conductor bars M0' and 100 torender them, respectively, anodic and cathodic. During movement of thesupport 26, it Will be clear that the brushes ll and |l8 will bealternately and periodically energized With anodic and cathodic current,respectively, by contact With the sections IH and 104 of the conductorbars ll and l00, and a periodically reversed current will be conductedto the base members 32 on the rack 28, whereby reverse current platingis carried out.

The insulation 4.2 shown in Fig. 2 of the drawings should have athickness sufiicient that the contact area of the support 26 does notexceed such thickness, otherwise shorting of current beu tween theSections 39 and 40 Will take place. For a similar reason, the insulatedsegments m0 and 108 in Fig. 3 should overlap in .the lengthwisedirection by an amount equal to at least the thiclrness of the brushes.

While carbon brushes have been shown in Fig. 3 of the drawings, metalliocontact members of various kinds may be employed. Since considerableamperage must flow from the conductor bars to the supports, the contactarea of the brushes, contacts or the like and the contact pressuresemployed. should be designed to take this fact into account.

The following is an example of a plating conveyor embodying the featuresof the invention. The total length of a conductor bar, similar to thebar 38 in Fig. l of the drawings, is 60 feet and it is divided into aseries of 60 Sections, each approximately 10 inches long, with anotherseries of 60 portions, each approximately 2 inches in length, a :2 inchportion being. inserted between each 10 inch section. The 2 inchportions are connected to a bus bar which is attached to the positiveterminal ofV direct-current generator. The conveyor comprises 24 movablework supports spaced approximately 2' 7 apart. Approximately 12,000amperes of cathodic current are passed ,to the cathodic portion of theconductor bar. The anodicV current flows in the proportion ofapproximately 10,000 amperes to ipermanent anodes o f copper similar tothe anodes |6, and 2,000 amperes to the anodic 2 inch portions insertedin the bus bar. The conveyor moves at a speed of 5 feet a minute,whereby base members are plated in approximately 12 minutes duringw'hich approximately 60 pulses of cathodic current deposit respectiveincrements of copper.

Each cathodic pulse lasts 10 seconds whilethe anodic current pulsedeplates unsound and inferior metal for 2 seconds. Due to the fact thatthe conveyor speed is variable, the cycle may be varied to provide forshorter or longer cathodic and anodic perods. However, the ratio ofcathodic to anodic pulses is fixed by the particular conductor barstructure.

In some cases it may be desirable to apply a materially increasedcurrent density to the anodic Sections or portions of the conductor barin order to deplate a larger proportion of the previusly platedincrement without however changing or unduly increasing the length ofthe conveyor. This may be accomplished conveniently by including anadditional source of direct current in the circuit in the mannerillustrated in Fig. 4 of the drawings. As illustrated, a maindirect-current generator 50 has its negative terminal 52` elcctricallyconnected by a bus 56 to the cathodic segments 39 of the conductor bar.The vpositive terminal 54 of the generator 50 is connected by a bus 58to the permanent anodes [6 of the metal being plated. An auxiliarydirect-current generator 64 of much smaller capacity than the generator50, for instance a generator having 20% of the output of the generator50, has its negative terminal 66 connected to the bus 56. An increase inthe cathodic current is thus applied to the cathodic Sections '30, ofthe conductor. The positive terminal 68 of the auxiliary generator 64 isconnected to a conductor 10 which is connected to the anodic Sections40. Anodic current flows from bus 58 through the conductor 60 to theconductor 10. In order to prevent anodic current from generator 64passing to the bus 58, a unidirectional valve or rectifier 62 is placedin the circuit formed by conductor 60. By regulating the output of thedirect-current generator 64, there accordingly may be secured apredetermined variable proportionality between the coulombs in anodicand cathodic pulses applied to the supports 26 and the work thereonduring their re- `spective times of contact with the Sections 39 |2 hasdisposed on each side thereof a pair of driving Wheels 132 moving incounterclockwise direction an endless belt |34 to which are afiixed lugsI 36 at predetermined intervals. 134. move loose copper support bars [46from The vlugs v right to left as seen in Figure 5. The copper bars 146are supported on the conductor bar 138 supported on insulating brackets144 having alternate cathodic Sections 139 and anodic sections 140constructed and functioning as described previously With respect toSections 39 and 40. At the start, each copper bar 143 is carriedmanually or by appropriate mechanism and laid on an insulated endsection 142 of the conductor bar 138. As the endless belt 134 moves thenext lug 136 into engagement With the copper bar, it moves Slidablyalong the length of the conductor bar 138 until the bar 146 reaches aterminal insulated section 143 when the lug 136 moves out of engagementwith the copper bar. The copper bar carries racks 148 which support basemembers 32 for electroplating. During the travel of the copper bar 146the length of the conductor bar 138 the base members 32 are subjected toalternate cathodic and anodic current pulses as the bar contactssections 139 and 140 successively Whereby the base members are plated byperiodic reverse current. At the end of the tank 130, the loose copperbars 136 are lifted by hand or by a suitable lifting mecham'sm forwashing or other further processing of the plated base members.

For some purposes the lengths of each of the respective Sections 39 and40, or 139 and 140, need not be constant throughout the entire length ofthe conductor bars. It may be found desirable to vary the lengths of theSections, as well as the ratios of the coulombs of anodic and cathodiccurrent supplied, as more metal is plated on the base members in orderto secure predetermined surface characteristics.

In some cases it may be desirable to provide an electrical circuitsupplied With electrical current from a single source of energy so thatthe current supplied the anodic Sections 40 may be varied in order tomodify the plating operation. Referring to Fig. 6 of the drawings, thereis'illustrated electrical members connected in electrical circui-trelation to a single source 200 of continuous direct current such as agenerator. The negative lead from the source 200 is connected byconductor 202 to the cathodic Sections 3-9. The positive lead from thesource 200 is connected by the conductor 204 to conductor 206 leading tothe anodio Sections 40 and conductor 210, in parallel therewith, to theanodes 15. The variable resistance 208 in conductor 206 and a secondvariable resistance 212 in conductor 210 enable the proportioning of thetotal anodic ampere output of the source 200 between the anodes 16 andanodic Sections within a predetermined range of values. The source 200ordinarily will operate at 'from 3 to 12 volts, and the resistances 208and 212 may 1be so constructed and operated to introduce a maximumresistance in each case of from about 1/0,000 to 1/100 of an ohm.However, the voltage and resistance may be varied in aocordance with thesize of the :plating installation, the metal being plated and otherfactors.

The advantages of the automatic electroplating conveyor arrangementdisclosed herein are several. They include a rapid reversal of currentfrom anodic to cathodic and vice versa with a minimum of time lost. Ithas been found that generators Operating on field reversal have asubstantial time lag in changing from maximum anodic to maximum cathodiccurrent output. Another advantage is that timing mechanisms and.contactors with their associated mainte- 8 1 nance problems areeliminated. The relatively' simple structures required for the conductorbars and slidable contacts as disclosed herein are such as will operateindefinitely 'With good results with a minimum of maintenance.Furthermore, substantially constant current conditions are realized,thus avoiding the violent current fluotuations which are met with Whenthe entire work in a tank is made Simultaneously anodic or cathodic. Thethrowing power of the electrolyte in the present invention is improved,since the work being plated is Surrounded on all sides with anodesduring the cathodic portion of the cycle.

Since certain obvious changes may be made in the above and differentembodiments of the invention may be constructed without departing fromthe scope thereof, it is intended that all the matter contained in theabove description and drawings be interpreted as illustrative and not ina limiting Sense. i

I claim as my invention:

1. In a conveyor electroplating machine for plating members with metalfrom anodes of the metal, in combination, a tank containing anelectrolyte, a plurality of Spaced movable supports having means thereonfor supporting members to be immersed in the electrolyte forelectroplating, means for moving the supports in one direction at apredetermined speed, contact means carried by each Support for supplyingelectrical current to members thereon, a relatively stationary conductormeans supported by the tank and disposed for Slidable contact with thecontact means on each support, the conductor means comprising a seriesof alternate electrically conducting surface Sections electricallyinsulated from each other, the Sections being so disposed andproportioned that every second one is shorter than the preceding sectionalong the direction of travel of the contact means with respect thereto,the series of shorter Sections having means for connecting them to theanodic terminal of a source of continuous direct current, the series oflonger Sections having means for connecting them to the cathodicterminal of a source of direct current, and the spacing between themovable supports being substantially uniform and So proportioned to thedimensions of the Sections that a relatively constant number of all thecontact means is in sliding contact With the shorter sections, whereby,in operation, a relatively constant anodic current is being supplied toless than half the supports and members being carried thereon and arelatively constant cathodic current is being supplied to more than halfthe supports and members being carried thereon, and, during movement ofa movable Support, any members supported thereon receive a successiveand alternating series of cathodic and anodic current pulses.

2. In an electroplating apparatus for plating members, a tank containingan electrolyte, a Support disposed above the tank having means thereonfor supporting the members, the Support being composed of anelectrically conducting metal, a bar carried by the tank upon which thesupport rests for slidable movement thereon, means for slidably movingthe Support along the bar, the bar comprising a plurality of insulatedelectrically conducting surface portions of unequal length arranged topresent alternate short and long Sections in contact With the support inits sliding movement, means for connecting the short sections to asource of continuous anodic auuaooo direct current and the long sectionsto a source of continuous cathodic current, whereby on movement of thesupport and its members on the bar it is subjected to a series ofalternating anodic current pulses for a short period of time andcathodic current for a longer period of time, and means attached to thetank for supporting a plurality of anodes of the metal to be plated onthe members.

3. In an electroplatng conveyor for plating members with metal from anelectrolyte in which is disposed an anode of the metal, in combination,a plurality of movable supports for supporting members to beelectroplated and for conducting electrical current to the members, eachsupport including an arm, suspending means on the arm for suspending inthe electrolyte the members being plated, means for conducting currentto the suspending means on the arm, and electrical insulation betweeneach arm and its neigh- `bors, means for moving the supportssubstantially continuously in a given path, a contact means associatedand movable with each support to supply the electrical current to themovable support, the contact means comprising a contact member on thearm connected in circuit relation with the means for conducting ourrentto the suspending means on the arm, a con- ,ductor bar located along thepath of movement,

of the movable support and positioned so as to be slidably contacted bythe contact means, the entire length of the conductor bar comprising aplurality of alternate electrically conducting cathodic and anodicsurface portions with insulation separating the portions, and meansconnecting a source of electrical current to the surface portions of thebar to render them anodic and cathodic respectively, whereby eachmovable support is rendered successively cathodic and anodic as itsassociated contact member passes over the alternate portions of theconductor bar during its movement.

4. In an electroplating conveyor for plating members with metal from anelectrolyte in which is disposed an anode of the metal, in combination,a plurality of movable supports for supporting members to beelectroplated and for conducting electrical current to the members, eachsupport including an arm, suspending means on the arm for suspending inVthe electrolyte the members being plated, means for conducting currentto the suspending means on the arm, and electrical insulation betweeneach arm and its neighbors, means for moving the supports substantiallycontinuously in a given path, a contact means associated and movablewith each support to supply the electrical current to the movablesupport, the contact means comprising a contact member on the armconnected in circuit relation with the means for conducting current tothe suspending means on the arm, a conductor bar located along the pathof movement of the 10 movable support and positioned so as to beslidably contacted by the contact means, the entire conductor barcomprising a plurality of alternate electrically conducting cathodic andanodic surface portions with insulation separating the portions, andmeans connecting a source of electrical current to the surface portionsof the bar to render them anodic and cathodic respectively, Whereby eachmovable support is rendered successively cathodic and anodic as itsassociated contact member passes over the alternate portions of theconductor bar during its movement.

5. In a conveyor plating machine for plating members with metal from anelectrolyte in which is disposed an anode of the metal, in combination,a plurality of spaced movable supports for supporting members to beelectroplated, each support including an arm, suspending means on thearm for suspending in the electrolyte the members being plated, meansfor conducting current to the suspending means on the arm and itsneighbors, and electrical insulation between each arm, means for movingthe support substantially continuously in a given path, contact means oneach support for supplying electrical current to the members thereonbeing plated, a relatively stationary conductor located along the pathof movement of the movable supports to be slidably contacted by thecontact means on each support, the stationary conductor having aplurality of electrically conducting cathodic and anodic surfaceportions disposed in alternate spaced arrangement with insulationseparating the portions for successive contact by each contact means,and means connecting a source of electrical current to the portions ofthe bar to render them anodic and cathodic respectively, whereby themembers on each support are rendered alternately cathodic and anodicduring movement of the movable supports, the spacing between thesupports being greater than and proportioned in relation to thedimensions of successive anodic and cathodic portions so that asubstantially Constant number of all the contact means are in contactwith the anodic portions, the anodic portions being shorter than thecathodic portions along the .direction of travel of the contact means.

GEORGE W. JERNSTEDT.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,574,055 Pedersen Feb. 23, 19261,769,188 Rabezzana July 1, 1930 1,809,139 Miller June 9, 1931 2,085,730Cox July 6, 1937 2,237,103 Lex Apr. 1, 1941

